FCC to minimize butadiene yields

Abstract

A process for fluidized catalytic cracking of heavy feed to make more catalytically cracked products and less thermally cracked products such as butadiene is disclosed. Operating an upflow riser reactor with a riser top temperature of 1050 to 1150 DEG F., and a short catalyst residence time, yields large volumes of gasoline and light olefins, but reduced yields of butadiene. Preferably cooled catalyst in large amounts contacts severely preheated feed. FCC catalyst with over 30 wt % Y zeolite is preferred.

I claim: 
     
       1. A process for the fluidized catalytic cracking of a feed containing hydrocarbons boiling above 650° F. comprising: a) preheating said feed to a temperature above 650° F. and sufficient to vaporize at least 50 wt % of said feed and produce a preheated feed;   b) charging to a base portion of a riser reactor said preheated feed and a stream of cooled, regenerated fluidized catalytic cracking catalyst containing at least 25 wt % large pore zeolite, based on the zeolite content of makeup catalyst to said cracking unit, and wherein the weight ratio of cooled, regenerated catalyst to preheated feed is at least 7.5:1 and produces a catalyst and feed mixture having a mix temperature of at least 1050° F. but below 1200° F.;   c) riser cracking said mixture in said riser reactor for a catalyst residence time of less than 1.5 seconds to produce a mixture of cracked products and spent catalyst which are discharged from an upper portion of said riser reactor at a riser top temperature between 1025° and 1125° F.;   d) separating said discharged mixture to produce a stream of catalytically cracked products which are removed as a product and a stream of spent catalyst containing entrained and absorbed catalytically cracked products and coke;   e) stripping said spent catalyst in a stripping means by contact with a stripping gas at stripping conditions to produce stripped catalyst;   f) regenerating said stripped catalyst in a catalyst regeneration means at catalyst regeneration conditions including a temperature above 1150° F. and contact with an oxygen containing gas to burn coke from spent catalyst, and produce regenerated catalyst having a temperature above 1150° F.; and   g) cooling said regenerated catalyst in a catalyst cooling means to produce cooled regenerated catalyst;   h) recycling said cooled regenerated catalyst to said cracking reactor to contact said feed.   
     
     
       2. The process of claim 1 wherein the mix temperature of catalyst and feed is at least 1075° F., and the catalyst has an average temperature in the reactor within the range of 1050° to 1100° F., and the catalyst has a residence time in the reactor of 0.5 to 1.0 seconds. 
     
     
       3. The process of claim 2 wherein the average catalyst temperature is 1065° to 1085° F. and the catalyst residence time is 0.65 to 0.85 seconds. 
     
     
       4. The process of claim 1 wherein the hydrocarbon feed is atomized into droplets below 500 microns when injected into said riser reactor. 
     
     
       5. The process of claim 1 wherein the hydrocarbon feed is atomized into droplets below 200 microns when injected into said riser reactor. 
     
     
       6. The process of claim 1 wherein the hydrocarbon feed is atomize into droplets below 100 microns when injected into said riser reactor. 
     
     
       7. The process of claim 1 wherein the feed is preheated to at least 750° F. 
     
     
       8. The process of claim 1 wherein the feed is preheated to at least 800° F. 
     
     
       9. The process of claim 1 wherein the catalytic cracking conditions include a catalyst to oil weight ratio of from 10:1 to 21:1. 
     
     
       10. The process of claim 1 wherein the catalytic cracking conditions include a catalyst to oil weight ratio of from 16:1 to 21:1. 
     
     
       11. The process of claim 1 wherein the feed is an atmospheric resid and contains at least 1.0 wt % Conradson Carbon Residue which readily forms coke at a temperature above 800° F., and said feed is preheated to a temperature of at least 800° F., and said catalyst regeneration conditions produce a regenerated catalyst having a temperature above 1300° F. which is cooled in a catalyst cooling means to a temperature of about 1075°-1150° F., and wherein the catalyst to oil weight ratio in said riser is at least 10:1, and the riser top temperature is about 1050°-1100° F. 
     
     
       12. The process of claim 1 wherein the butadiene content of the cracked product is at least periodically measured and at least one of the cracking reactor catalyst residence time and average reactor temperature are changed in response to said butadiene content. 
     
     
       13. A method of cracking a heavy feed comprising at least 10 wt % hydrocarbons not recoverable by distillation at atmospheric pressure to catalytically cracked products including at least 50 LV % gasoline and less than 0.15 wt % butadiene based on weight of fresh feed to said cracking reactor, comprising: a) preheating said feed to a temperature above 700° F.;   b) contacting in the base of a riser reactor said preheated feed with a stream of cooled fluidized catalytic cracking catalyst containing at least 30 wt % Y zeolite, based on the Y zeolite content of makeup catalyst to said cracking unit, to produce a catalyst and feed mixture having a temperature of 1050° F. to 1150° F.;   c) riser cracking said mixture for a catalyst residence time of 0.5 to 1.0 seconds to produce a mixture of cracked products and spent catalyst which are discharged at a reactor outlet temperature, and wherein the reaction conditions include a cat:oil weight ratio above 10:1 and a riser reactor outlet temperature of 1050° to 1100° F.;   d) separating said mixture to produce a stream of catalytically cracked products which are removed as a product and a stream of spent catalyst containing entrained and absorbed catalytically cracked products and coke;   e) analyzing at least the C4+portion of said cracked products to determine the gasoline yield and the butadiene content thereof and reducing reaction severity by adjusting at least one of the catalyst residence time and riser outlet temperature in response to said butadiene when butadiene content increases above a predetermined level below 1500 wt ppm of feed, and increasing reaction severity when gasoline yield decreases below a predetermined level equal to at least 50 LV % of fresh feed;   f) stripping said spent catalyst in a stripping means by contact with a stripping gas at stripping conditions to produce stripped catalyst;   g) regenerating said stripped catalyst in a catalyst regeneration means at catalyst regeneration conditions including contact with an oxygen containing gas to produce regenerated catalyst having a temperature above 1300° F.;   h) cooling, in a catalyst cooling means, said regenerated catalyst, to produce cooled regenerated catalyst having a temperature below 1200° F.; and   h) recycling said cooled regenerated catalyst to said cracking reactor to contact said feed.   
     
     
       14. The process of claim 13 wherein the reaction severity is reduced when butadiene content increases above 1000 wt ppm. 
     
     
       15. The process of claim 13 wherein the gasoline is the C5-12 portion of the catalytically cracked products. 
     
     
       16. The process of claim 13 wherein the mix temperature of catalyst and feed in the riser is 1065° to 1085° F. and the catalyst residence time is 0.65 to 0.85 seconds and the catalyst has a zeolite Y content of at least 40 wt %, based on the Y zeolite content of makeup catalyst. 
     
     
       17. The process of claim 13 wherein the hydrocarbon feed is atomized into droplets below 200 microns when injected into said riser reactor. 
     
     
       18. The process of claim 13 wherein the feed is preheated to at least 750° F. 
     
     
       19. The process of claim 13 wherein the feed contains more than 2.0 wt % CCR, and the catalytic cracking conditions include a catalyst to oil weight ratio of from 10:1 to 21:1. 
     
     
       20. The process of claim 13 wherein the catalytic cracking conditions include a catalyst to oil weight ratio of from 16:1 to 21:1.